WO2013089546A1

WO2013089546A1 - Method for treating furnace dust from a steelmaking electric-arc furnace

Info

Publication number: WO2013089546A1
Application number: PCT/MX2012/000125
Authority: WO
Inventors: Juan Antonio VILLARREAL TREVIÑO; Alejandro MONTESINOS CASTELLANOS; Gustavo LEON CAZARES
Original assignee: Instituto Tecnologico Y De Estudios Superiores De Monterrey; Ternium Mexico S.A. De C.V.
Priority date: 2011-12-14
Filing date: 2012-12-10
Publication date: 2013-06-20
Also published as: MX2011013573A

Abstract

The invention relates to a method and system for the chemical treatment of dust from an electric-arc furnace, which is contained in the gases formed in said electric furnace during the steelmaking process, in order to reduce the water solubility of the metal oxides contained in said dust, and thus to reduce the environmental problems due to the toxicity of same. The method includes extracting the high-temperature gases that contain the dust from said furnace in addition to carbon dioxide; placing the gases that contain dust in contact with a first stream of water in a first contact container in order to draw the dust from the gases into said stream of water; extracting the stream of water that carries said dust and feeding same into a second container such as to form a mixture of said powders with water having a controlled alkalinity of 7.5 to 8.5; extracting from said second container a stream of the mixture of dust and water formed by said first stream of water, and feeding said mixture of water and dust into said first container in order to place in contact and promote the reaction between the dust contained in said stream of water and the carbon dioxide contained in the gases extracted from the electric furnace.

Description

METHOD FOR TREATMENT OF ARCH OVEN POWDER

ACERATION ELECTRIC

Field of the Invention

The present invention relates to the field of the steel industry and steel manufacturing, more particularly, the invention relates to a process and a system for the treatment of dusts that are generated in electric arc furnaces during melting and Refining ferrous materials to eliminate the toxic nature of these powders and facilitate their handling and storage or disposal without damaging the environment.

BACKGROUND OF THE INVENTION In the operation of the electric arc furnace for steel manufacturing, the gases generated by the fusion of the ferrous materials scrap and / or direct reduction iron (known as DRI, and also as sponge iron), are extracted to through the so-called "fourth hole" located on the oven lid. These gases carry powders containing various metal oxides derived from scrap metal, from direct reduction iron and from the additives that are added for slag formation.

The composition of electric acceleration furnace powders comprises zinc and other toxic heavy metals, which makes them difficult to recycle and dispose of, causing high storage and special care costs for disposal, due to the risk of leaching of the metals contained therein.

The amount of dusts generated in steelmaking is estimated between 0.4% and 3.2% of the tons of steel produced, which represents an additional cost of more than $ 2 per ton of steel.

Several processes for the treatment of electric oven powders have been found in the prior art to make them less toxic and harmful to the environment and therefore decrease the costs related to their storage and disposal.

US Patent 5,569,152 describes a method and composition for treating electric arc furnace powders so that already treated powders can be discarded without environmental toxicity problems. The teaching of this patent is to form a cementitious composition by adding to the electric furnace, iron sulfate, lime and water powders and in addition a pH regulating or buffering agent such as di-hydrated dolomitic lime or hydrated lime is added. The neutralizing agent may be sulfuric acid. It also mentions that the neutralizing agent can be carbon dioxide, however it does not describe or suggest a practical method for reacting the powders with carbon dioxide. A disadvantage of this process is that it is required to add ferrous sulfate in significant amounts, which increases the cost of treatment both by the amount consumed and by the increase in waste volume. US Patent 6,991, 593 describes a method for stabilization of metal-containing residues by adjusting the pH, using HCL, H2S0 ₄ or H ₃ P0 ₄ and a reducing agent containing sulphides (sodium sulphite) for the medium be reductive. In this way the powders become non-leachable in the places where they are stored, making them suitable for storage in landfills. The pH of the mixture of powders and water should be between 8.5 and 12.5.

European Patent 0 363 429 describes a method for chemically stabilizing electric furnace powders using the following reagents: "Fly Ash", S0 ₂ and Al ₂ 0 ₃ ; CaO lime powder; Hydrated lime CaOH and hepta-hydrated iron sulfate.

This process forms a concrete-like product with powders and these reagents.

The patents mentioned above are incorporated into this description of the invention by reference. Objectives of the invention

It is therefore an objective of the present invention to provide a method and apparatus for stabilizing electric arc furnace powders so that they are not harmful to the environment and can be disposed of at low cost.

It is another object of the present invention to provide a method and apparatus for stabilizing electric arc furnace powders using carbon dioxide produced by said electric arc furnace as a stabilizing agent and thus reducing the amount of carbon dioxide emitted into the atmosphere in plants Steel manufacturing.

Brief Description of the Drawings Figure 1 shows a schematic diagram of a preferred embodiment of the process of the invention.

Detailed description of the invention

The electric arc furnace powders used for the manufacture of steel, contain metal oxides that come from the ferrous material used as raw material for the manufacture of steel and in the case of using iron scrap, the melting materials that are added to the load to form the slag necessary for the adjustment of the chemical composition of the iron bath that is transformed into steel.

Typically between 15 and 30 kg of powders are produced per ton of liquid steel, so the problem presented by the toxicity of these powders is important in the steel industry.

The chemical composition of the powders varies according to the type of raw material used for the manufacture of steel and the materials added to the metal filler as fluxes and to form a slag layer that helps eliminate undesirable chemical elements in the final composition. of manufactured steel. The raw material can be steel scrap or direct reduction iron (DRI), also known as sponge iron, which has between approximately 60% and 70% iron oxides and approximately 5% to 10% other metal oxides.

With reference to figure 1, numeral 10 generally designates an electric arc furnace for the manufacture of steel. Ferrous materials that can be steel scrap, direct reduction iron (HRD), iron briquettes (HBI), cast iron in solid or liquid form, or mixtures of these materials in addition to lime, ferroalloys and other materials to produce are baked in the oven the steel. A typical composition of electric oven powders for steelmaking is as follows:

(% by weight) Oven 1 Oven 2 Oven 3 Oven 4

Sodium Oxide 3.81 4.12 1 .132 3.216

Potassium Oxide 0 0 0.843 4.095

Magnesium Oxide 5.71 7.25 4,973 5,719

Aluminum Oxide 0.9 1 .03 0.944 1 .474

Calcium Oxide 5.6 5.92 6.44 5.6

Chrome Oxide 0.059 0.18 0 0

Iron Oxide 71 .5 61 .1 26.77 50.33

Manganese Oxide 0.95 1 .45 4,938 1 .04

Nickel Oxide 0.0032 0.0055 0 0

Copper Oxide 0.033 0.049 0 0

Zinc Oxide 7.44 13.1 39.84 12.3

Silver Oxide 0.0008 0.0008 0 0

Cadmium Oxide 0.0008 0.0017 0 0

Lead Oxide 0.065 0.21 1 .378 0.866

Silicon Oxide 0.14 0.15 5,075 4,754

Mercury Oxide 0.00008 0 0 0

Barium Oxide 0.0039 0 0 0

During the melting process, and in its case of refining, of the materials in the furnace, high temperature gases 12 are formed which are extracted by a pipeline water cooled 14. The hot gases with powders derived from the ferrous materials fed to the furnace are combined with air injected by the duct 16 to transform the CO present in said gases to CO ₂ and pass to a powder settling chamber 18 to separate large particles of dusts 19 and gases with fine dusts 20. Large particles of dust 19 are periodically extracted from said chamber 18 and taken to sedimentation pits 22.

Dust gases pass from the duct 23 to a container 28 where they are put in contact with a mixture (such as a light fluid sludge) of dusts and water that are fed by the tubes 30 and 33 to a nozzle 32 that splashes water with dusts and in this way the powders come into contact and react with the CO2 of the gases extracted from the oven.

Through this contact, the gases are cleaned of the dusts and leave the container 28 through the duct 34 to filters or "baghouse" 36 where they are completely cleaned of dusts before being expelled into the atmosphere by a suitable chimney 42 in a known manner in art

Metal oxides that are considered toxic are converted to carbonates with the CO2 from the gases in the electric furnace, so they are no longer soluble in water and leaching is avoided and can be stored in the open field.

After contacting the mixture of powders and water in the container 28, the gases pass through the tube 34 to the filters 36 where the smaller dust particles 38 are separated, which are optionally passed to the sedimentation pit 22 to integrate the treated powders 40 that are extracted from the sedimentation pit 22 to be stored in the open field. Once the gases are filtered in the filters 36, they are expelled into the atmosphere by a suitable chimney 42, in a manner known in the art.

From the settling pit 22, a stream of dusts and water is taken through the tube 44 and fed through a pump 46 and a tube 48 to a stirred tank 50 provided with a stirrer 52 to form a light sludge that can be flow through the tube 54 and the pump 56 into the container 28 where it is sprayed and comes into contact with the gases containing CO2 by means of the nozzles 29. Water is added in a regulated amount to the stirred tank 50 by the tube 62 in sufficient quantity so that the mixture of powders and water has an adequate fluidity to be spilled in the contact vessel 28. The mixture of powders and water with a controlled pH that comes into contact with the gases containing carbon dioxide in the vessel 28 , it is removed by the tube 31 and recirculated to the stirred tank 50. A portion of the light sludge of dusts and water can also be used to lower the temperature of the hot gases of the furnace by means of the tube 26 and a venturi tube 24.

Optionally a portion of the mixture of powders and water can be passed from the stirred vessel 50 to the sedimentation pit 22 by means of the tube 58 provided with a valve 60 to sediment the already treated powders and extract them for disposal as non-toxic products. When the pH in the stirred vessel 50 reaches a predetermined level, between 7.5 and 8.5, the fluid sludge is removed from the treatment tank and passed to filters or sedimentation pits so that once separated from the water, it is transported to normal places for its accumulation since once treated it is not considered as toxic material.

Due to the different metal charges in each steel mill, different quantities and compositions are produced in the powders produced by each electric furnace, impacting on different theoretical CO2 retention capacities.

Typically, an electric steelmaking furnace generates approximately 50 tons of CO2 per hour and 2.2 metric tons of dusts, so approximately 0.85 metric tons of CO2 per day would be captured with the dusts generated in that oven.

Example 1 .

A solution of 33.5% by weight of powders was prepared, mixing 101 g of powders and 200g of water. A mixture of air and CO2 was fed to the device and its output composition was analyzed with a gas chromatograph.

It was determined that for every m ³ of solution powders were captured 8,400 kg CO2, 4,667 m ³ equivalents of C02 and 0025 g of CO2 per gram of powder. Example 2

A solution of 33.5% by weight of powders was prepared, mixing 101 g of powders and 200g of water. A mixture of air and C0 ₂ was fed to the device and outlet composition was analyzed with a gas chromatograph.

It was determined that for each m ³ of aqueous powder solution, 5,457 kg of C0 ₂ were captured, equivalent to 3,032 m ³ of C0 ₂ and 0.016 g of C0 ₂ per gram of powders.

The amount of C0 ₂ removed from the furnace gases by acid-base reaction in aqueous medium, measured in Kg of C0 ₂ / metric ton of liquid metal, has been estimated in the following range:

Test 1 Test 2 Test 3 Test 4

Minimum 6.41 4.60 3.22 5.71

Maximum 23.80 14.82 12.42 16.13

This amount of C0 ₂ is prevented expel the atmosphere is important to help industry steelmaking to comply with environmental regulations and environmental both the emissions into the atmosphere as for handling dust generated in said steelmaking process. An advantage of the present invention is that the neutralization of the toxic metals of the powders is carried out with CO ₂ that is generated in the same furnace that produces the powders, and that reacts with the metal hydroxides transforming to carbonates that are retained in previously treated powders, thus reducing the amount of C0 ₂ emitted into the atmosphere.

With this treatment, the dusts that are ordinarily considered as toxic material and that have to be confined in special places, are no longer toxic materials or waste and can be freely disposed of, significantly reducing current costs for handling, storage and special confinement of these powder.

The capital and operating costs of this process to neutralize the acceleration furnace powders are relatively very low compared to other processes that require purchase of more sophisticated chemical reagents and equipment.

It is understood that only some of the preferred embodiments of the invention have been described herein and that many changes can be made to the described modalities, as the invention best suits a particular use, without departing from the spirit and scope thereof, which It is defined in the attached claims.

Claims

CLAIMS Having described the invention, it is considered a novelty and claims as contained in the following clauses:

1. A method for the treatment of electric arc furnace powders carried by the gases formed in said furnace during the steelmaking process, to decrease the water solubility of the metal oxides contained in said powders, and thus decrease the environmental problems caused by its toxicity, said method being characterized in that it comprises: extracting from said electric oven the high temperature gases containing said dusts and also carbon dioxide; contacting the gases containing said dusts with a stream of water containing dusts that is circulated in a circuit comprising a first contact vessel for dragging the dusts of the gases into said water stream; extracting from the first vessel a second stream of water that draws said powders and feeding it to a second vessel to form a mixture of said powders and water with a controlled alkalinity; extracting from said second vessel a stream of the mixture of powders and water with a pH value between 7.5 and 8.5; feed at least a portion of said mixture of water and powders to the first container and promote contact and reaction of the powders contained therein second stream of water with carbon dioxide contained in the gases extracted from the oven.

2. The method according to claim 1, characterized in that it further comprises injecting air into said gases extracted from the electric furnace to at least partially convert the carbon monoxide they contain to carbon dioxide.

3. A method according to claim 1, characterized in that it further comprises stirring the mixture of powders and water in said second container to form a fluid sludge that can be conducted by means of a pump and sprinkled into said first container.

4. A method according to claim 1 characterized in that it further comprises maintaining the pH of said first stream of the mixture of water and powders at a value between 7.5 and 8.5.

5. A method according to claim 3, characterized in that it further comprises transferring the light sludge from the agitated tank to a sedimentation tank to separate the already treated powders and dispose of them as non-toxic waste.

6. A system for the treatment of electric arc furnace powders entrained by the gases that form in said furnace during the steel manufacturing process, to reduce the water solubility of the metal oxides contained in said powders, and thus reduce the environmental problems caused by their toxicity, said system being characterized by comprising: a first pipeline in communication with said electric furnace by which the high temperature gases containing said powders and also carbon dioxide are extracted; a first container for contacting the gases containing said powders with a stream of water containing powders; means for circulating said stream containing dusts in a circuit comprising said first contact vessel for dragging the dusts of the gases into said stream of water; a second vessel provided with means for stirring a mixture of water with powders; means for feeding at least a portion of said mixture of water and powders to the first container where contact and reaction of the powders contained in said second stream of water is promoted with the carbon dioxide contained in the gases extracted from the oven; filter means for filtering powders carried by the effluent gases of said first container; a sedimentation tank where the powders already treated are separated; and the ducts connecting said first container with said second container and with said sedimentation tank to form a recirculation circuit of the mixture of powders and water.

7. A system according to claim 6, further characterized by comprising means for measuring the pH of the content of said second container to control its pH in a range between 7.5 and 8.5.

8. A system according to claim 6, further characterized in that said filter media is a baghouse.

9. A system according to claim 6, further characterized by comprising a third container connected to said electric furnace where the larger powders of the gases are separated at high temperature by speed reduction of said gases.